Rolled tissue products, as well as other rolled paper or nonwoven products, are typically perforated (“perfed”) in order to facilitate the tearing off of the desired length of product for the intended use in a neat and undamaged fashion. In tissue products, the perforations facilitate easy removal of the required number of sheets. The perforations are normally provided in transverse perforation lines across the roll width, which are uniformly spaced in the machine direction of the roll. The lines of perforations comprise alternating bonds and perfs which are of uniform length and spacing. The perfs are typically rectangular slits or round holes with transverse orientation.
Perforating devices are well known in the papermaking art and are incorporated into almost all bathroom tissue and towel winders as well as other converting equipment in a typical tissue manufacturing and converting plant. In the past, conventional devices typically comprised a perforator roll, which holds a number of perf blades, and a stationary anvil head.
In the converting process, a balance must be struck between having perforation lines that have sufficient bond strength to operate efficiently and without breaks on the converting equipment, and yet have low enough bond strength to provide easy and undamaged sheet detaching for the consumer. Nevertheless, in spite of efforts to achieve this proper balance, poor detaching has been the subject of various consumer complaints for rolled tissue products such as toilet tissue or kitchen towels.
The above problems become exacerbated when attempting to perforate thicker, heavier and multiple-ply tissue sheets. Thicker and heavier tissue sheets, for instance, are more difficult to perforate cleanly and efficiently. The tissue sheet tends to be grabbed by the perf blade or gets stuck in the perf blade which can create uneven perforations or tearing of the sheet.
In view of the above, a need exists for a new method and apparatus for perforating tissue sheets, especially thicker and heavier tissue sheets.